87Bb Cu Settings (Compensated Earthed Network Schemes) - GE P741 Technical Manual

P74x/EN AP/Na7
(AP) 6-8
AP
2.1.1.2

87BB CU Settings (Compensated Earthed Network Schemes)

2.1.1.2.1 Sub-station features
Only 4 values have to be known:
1.
2.
3.
4.
2.1.1.2.2 Differential Busbar Protection
9 values have to be chosen:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Explanations of the values:
1.
2.
• the maximum load is on the 2 buses (biggest bias current)
• The internal short-circuit value is minimum.
During the internal fault:
• the CZ bias current is:
• the CZ differential current is:
Thus the biggest slope for the Check Zone to detect the fault is:
(4 x IloadMax (1 bar)) + Icc min (1 bar)
If for example:
Icc min = IloadMax, the slope must be below 20%
b) Recommendation is 25% for China
In china, the requirement is to be able to trip for a resistive fault that is counted
twice by the Check Zone (for example one and half circuit breaker substation).
−
ID>1 Alarm Timer to not operate for an external fault shall be greater than the
longest protection time (such as line, overcurrent, etc...)
Maximum load current in a feeder
Minimum phase to phase fault current (Ph-Ph min.) in a bus
Maximum single phase steady state faulty current (Ph-N Max.) in a bus
Number of independent bars
ID>1 (from 5 A to 500 A (primary value)), recommendation equal to 1,2 x (Ph-N Max.)
Slope k1 (ID>1) (from 0% to 50%), recommendation is 10%.
ID>1 Alarm Timer (from 0 to 100 s) shall be greater than the longest Busbar protection
time
Slope k2 (from 20% to 90%) but recommendation 65%.
ID>2 (from 50 A to 50000 A (primary value)), recommendation is:
Lower than 0,8 x (Ph-Ph min) and Higher than 1,2 x Iload Max and if possible equal to
6 x (ID>1).
Slope kCZ (from 0% to 90%) but recommendation 30%.
IDCZ>2 (from 50 A to 50000 A (primary value)), recommendation is:
Lower than 0,8 x (Ph-Ph min) and Higher than 1,2 x Iload Max and if possible equal to
6 x (ID>1).
ID>1 shall be higher than 120% of the highest phase to neutral fault to not operate in
case of phase to neutral fault.
Slope k1 recommendation is 10% to meet 10Pxx current transformers
Icc min (1 bar) + 4 x IloadMax (1 bar)
Icc min (1 bar)
Icc min (1 bar)
Application Notes
MiCOM P741, P742, P743